1. Field of the Invention
The present application relates to measurement machines, more specifically to articulated arm portable coordinate measurement machines.
2. Description of the Related Art
Portable coordinate measurement machines (PCMMs) such as articulated arm PCMMs can be used to perform a variety of measurement and coordinate acquisition tasks. In one common commercially-available PCMM, an articulated arm having three transfer members connected by articulating joints allows easy movement of a probe head about seven axes to take various measurements. For optimal precision and accuracy of the measurements generated by a PCMM, it must initially be calibrated to account for any manufacturing variations in the components of the PCMM itself.
Previously, a portable coordinate measurement machine would be calibrated by using the PCMM to measure one or more length artifacts such as bars of precisely known dimensions. By using a PCMM to measure lengths of a length artifact having precisely known dimensions, position data obtained by the PCMM could be analyzed, and a PCMM processor and or position measuring device such as an analog or digital encoder calibrated to reflect the known measurements of the length artifact.
While the previous calibration process typically resulted in acceptable calibration results, it did have shortcomings. The prior PCMM calibration process can be expensive as the precision-manufactured length artifacts are difficult and costly to produce. This previous calibration process was also time consuming as the PCMM would need to be manually manipulated between various positions with respect to the length artifacts. The prior PCMM calibration process was also somewhat limited as only a relatively small number of position readings were typically taken. Also this process can be subject to some variation as even the precision-manufactured length artifacts are subject to some degree of length variation due to thermal expansion.